Base station apparatus, communication control system, communication control method, and inter-station control method

ABSTRACT

A base station apparatus includes a determining unit that determines whether a direct link has been established between the base station apparatus and another base station apparatus, when a mobile device makes a request to switch a communication recipient from the base station apparatus to the other base station apparatus; a link information acquiring unit that acquires, indirectly from the other base station apparatus, link information necessary for establishing the direct link to the other base station apparatus, when the determining unit determines that no direct link to the other base station apparatus has been established; and a link requesting unit that requests the other base station apparatus to establish the direct link to the base station apparatus, based on the link information of the other base station apparatus acquired by the link information acquiring unit.

CROSS-REFERENCE TO RELATED APPLICATION(S)

This application is based upon and claims the benefit of priority of theprior Japanese Patent Application No. 2008-239952, filed on Sep. 18,2008, the entire contents of which are incorporated herein by reference.

FIELD

The embodiments are discussed herein are directed to a base stationapparatus, a communication control system, a communication controlmethod, and an inter-station control method that can reduce theprocessing load imposed on an evolved packet core (EPC) on each handoverbetween wireless base stations.

BACKGROUND

To make a smooth migration from the third generation (3G) mobilecommunication to the fourth generation (4G) mobile communication, a longterm evolution (LTE: super 3G) has been developed as a standard forhigh-speed mobile communication. Although the LTE is regarded as anevolution of the international mobile telecommunications (IMT)-2000, awireless interface and a radio access controller (RAC) architecture ofthe 3G system have been reexamined fundamentally to make a smoothmigration to the 4G. As a result, with delay time compression andimprovement in communication speed, the LTE achieves maximum datacommunication speed of 300 megabits per second for downloading, and of50 megabits per second for uploading.

Mobile communication systems according to the LTE have undergone somechanges in nodes from the current 3G systems. Specifically, because aplurality of wireless base stations is centrally managed by an evolvedpacket core (EPC), radio network controllers (RNCs) provided inconventional 3G systems are omitted and most functions of the RNCs areprovided in the wireless base stations.

In communication between wireless base stations according to the LTE, amessage in an S1 protocol is used when the communication is performedthrough the EPC, while a message in an X2 protocol is used when thecommunication is performed not through the EPC, as specified in therecommendations of the third generation partnership project (3GPP). Touse such messages in the X2 protocol and the S1 protocol, it isnecessary for each wireless base station to establish setting links toanother wireless base station to communicate with and to the EPC,respectively.

In general, such an inter-station link is set or removed when a wirelessbase station is set up, or when the number of neighboring wireless basestations is increased or decreased. Desirably, inter-station links areset for all of the neighboring base stations. Under existingcircumstances, however, when inter-station links are set for manyneighboring wireless base stations, the processes for setting theinter-station links are increased, thus causing time delay in restartingmobile communication interrupted during the setting. Further, when manyinter-station links are set, resources necessary for setting theinter-base links run out because they are limited. For these reasons,attempts have been made to reduce the number of neighboring wirelessbase stations for which inter-station links are set as much as possible.

Considering the existing circumstances for setting the inter-stationlinks, the recommendations of the 3GPP define a process for switching awireless link between a mobile device and a wireless base stationaccording to movement of the mobile device, when the mobile device movesfrom a wireless base station to another wireless base station (theprocess is referred to as “handover”). Specifically, the 3GPP defines:X2 handover using an inter-station link between wireless base stations;and S1 handover using an inter-station link between a wireless basestation and an EPC, either of which is used according to the movement ofa mobile device from a wireless base station to another wireless basestation.

Referring to FIG. 16, the following describes operations of handover inmobile communication using the LTE. As shown in FIG. 16, in the mobilecommunication system using the LTE, a plurality of wireless basestations (A, B, X, Y, and C) is directly connected to an EPC, and aninter-station link is set between each of the wireless base stations andthe EPC. The wireless base station X has an inter-station link to thewireless base station A, while having no inter-station link to the otherwireless base stations B, Y, and C. In this situation, for example, whena mobile device being in wireless communication with the wireless basestation X moves into a control region of the wireless base station A, X2handover is performed because the wireless base station A has aninter-station link to the wireless base station X. On the contrary, whena mobile device being in wireless communication with the wireless basestation X moves into a control region of the wireless base station C, X2handover cannot be performed and S1 handover is performed because thewireless base station C has no inter-station link to the wireless basestation X.

The PCT International Publication WO99/34627 Pamphlet discloses thefollowing technology. Assume that a mobile device being in wirelesscommunication with the wireless base station X moves into a region whereno wireless base station exists as a recipient of handover. In thiscase, by reducing the number of handover requests regularly made by themobile device, the voice interruption caused by handover operations isreduced. In this way, the communication quality is improved between themobile device and a wireless base station.

When handover is made from a wireless base station being in wirelesscommunication with many mobile devices to another wireless base stationhaving no inter-station link to the wireless base station, S1 handoveris performed for every handover. This poses a problem of increasing theprocessing load on the EPC.

Referring to FIG. 17, the following describes the problem regarding theload on the EPC in detail. As shown in FIG. 17, the wireless basestations X and C each have an inter-station link to the EPC, whilehaving no inter-station link therebetween. In this situation, when manymobile devices being in wireless communication with the wireless basestation X move into a control region of the wireless base station C, thewireless base stations X and C cannot perform X2 handover because nointer-station link has been set therebetween. Thus, the wireless basestations X and C perform S1 handover every time such a mobile devicemoves in. This increases the processes for performing S1 handover in theEPC, thus increasing the processing load thereon.

Particularly in the LTE, it is assumed that one EPC controls manywireless base stations. When a plurality of wireless base stations makesmany requests for S1 handover at one time, the EPC has a furtherincreased processing load. As a result, the handover may fail, degradingthe services to be provided to existing callers.

SUMMARY

According to an aspect of the invention, a base station apparatusincludes a determining unit that determines whether a direct link hasbeen established between the base station apparatus and another basestation apparatus, when a mobile device makes a request to switch acommunication recipient from the base station apparatus to the otherbase station apparatus; a link information acquiring unit that acquires,indirectly from the other base station apparatus, link informationnecessary for establishing the direct link to the other base stationapparatus, when the determining unit determines that no direct link tothe other base station apparatus has been established; and a linkrequesting unit that requests the other base station apparatus toestablish the direct link to the base station apparatus, based on thelink information of the other base station apparatus acquired by thelink information acquiring unit.

The object and advantages of the invention will be realized and attainedby means of the elements and combinations particularly pointed out inthe claims.

It is to be understood that both the foregoing general description andthe following detailed description are exemplary and explanatory and arenot restrictive of the invention, as claimed.

BRIEF DESCRIPTION OF DRAWING(S)

FIG. 1 is a schematic of an entire communication control systemaccording to a first embodiment of the present invention;

FIG. 2 is a schematic of a protocol stack of S1 protocols;

FIG. 3 is a schematic of a protocol stack of X2 protocols;

FIG. 4 is a simplified sequence diagram of a procedure of S1 handover;

FIG. 5 is a simplified sequence diagram of a procedure of X2 handover;

FIG. 6 is a functional block diagram of the entire communication controlsystem shown in FIG. 1;

FIG. 7 depicts a data structure of wireless base station information;

FIG. 8 depicts a data structure of handover execution information;

FIG. 9 is a sequence diagram of a handover procedure performed by thecommunication control system shown in FIG. 1;

FIG. 10 is a sequence diagram of a procedure for setting aninter-station link in the communication control system shown in FIG. 1;

FIG. 11 is a flowchart of a process for determining an inter-stationlink setting request according to the first embodiment;

FIG. 12 is a functional block diagram of an entire communication controlsystem according to a second embodiment of the present invention;

FIG. 13 is a sequence diagram of a handover procedure performed by thecommunication control system shown in FIG. 12;

FIG. 14 is a sequence diagram of a procedure for removing aninter-station link in the communication control system shown in FIG. 12;

FIG. 15 is a flowchart of the process for determining an inter-stationlink removal request according to the second embodiment;

FIG. 16 is a drawing for explaining conventional handover operations;and

FIG. 17 is a drawing depicting a problem of conventional handoveroperations.

DESCRIPTION OF EMBODIMENT(S)

Preferred embodiments of a wireless base station and a communicationcontrol system that use an LTE according to the present invention aredescribed in detail with reference to the accompanying drawings. Thepresent invention is not limited to the embodiments.

[a] First Embodiment

FIG. 1 is a schematic of an entire communication control systemaccording to a first embodiment of the present invention. As shown inFIG. 1, the communication control system includes an EPC, a plurality ofwireless base stations A, B, C, X, and Y, and mobile communicationterminals.

Through wired communication, the EPC controls paths and datatransmission and reception between wireless base stations allocated inits control region. For example, when a mobile communication terminalmakes a handover from a wireless base station to another wireless basestation, the EPC controls transmission and reception of messages betweenthe wireless base stations for the handover, and switches the wired path(path switching).

Each mobile communication terminal transmits and receives a message toand from a wireless base station with which the mobile communicationterminal is in wireless communication. For example, when making ahandover from a wireless base station to another wireless base station,the mobile communication terminal transmits a handover requestrequesting switching of the wireless path to a wireless base stationwith which the mobile communication terminal is in wirelesscommunication. From the wireless base station having received thehandover request, the mobile communication terminal receives a responseto the handover request, establishes a wireless path to a new wirelessbase station, and transmits a handover completion notification,indicating the completion of switching the wireless path, to the newwireless base station using the established wireless path. Although themobile communication terminal is described as a mobile telephone, themobile communication terminal may be a personal computer, a workstation,a home game console, an internet television (TV), a personal digitalassistant (PDA), a portable telephone, a personal handyphone system(PHS), or other type of mobile communication terminal widely available.

The wireless base stations A, B, C, X, and Y are allocated in a controlregion of the EPC, and each have an inter-station link in an S1 protocolto communicate with a neighboring wireless base station through the EPC.Thus, the wireless base station X communicates with its neighboringwireless base station Y through the EPC. Further, the wireless basestation X has an inter-station link in an X2 protocol to communicatedirectly with its neighboring wireless base station, for example withthe wireless base station A or B. This allows the wireless base stationX to communicate with its neighboring wireless base station A or B notthrough the EPC. Each of the wireless base stations allocated in thecontrol region of the EPC has an inter-station link in the S1 protocolto the EPC.

Assume that a mobile communication terminal switches a communicationrecipient from the wireless base station X to the wireless base stationY. In this case, when no inter-station link in the X2 protocol has beenset to the wireless base station Y, the wireless base station Xacquires, from the wireless base station Y through the EPC, settinginformation necessary for setting an inter-station link in the X2protocol to the wireless base station Y. The wireless base station Xthen makes a request to set an inter-station link in the X2 protocol tothe wireless base station Y by using the setting information acquiredfrom the wireless base station Y, and the wireless base station Y setsan inter-station link in the X2 protocol to the wireless base station X.This enables the wireless base station X to transmit and receive amessage directly to and from the wireless base station Y. Thus, thewireless base station X can exchange a message directly with thewireless base station Y in the next handover. This reduces theprocessing load to be imposed on the EPC on each handover. The processesperformed by the wireless base stations X and Y will be described indetail later.

Referring to FIGS. 2 and 3, the following describes a protocol stack ofS1 protocols specifying an inter-station link between the EPC and eachwireless base station, and a protocol stack of X2 protocols specifyingan inter-station link between wireless base stations. The S1 protocoland the X2 protocol are specified in the recommendations of the 3GPP.

FIG. 2 is a schematic of a protocol stack of S1 protocols. As shown inFIG. 2, the bottom layer is physical layer software such as a devicedriver, on which data link layer software, network layer software suchas an internet protocol (IP), and a transport layer, i.e., a streamcontrol transmission protocol (SCTP) are stacked in this order frombottom to top. The S1 application software in the top application layersets an SCTP link (inter-station link) to the EPC, thereby communicatingwith the EPC by using messages in the S1 protocol. As a result, thewireless base station X performs handover with the wireless base stationY through the EPC by using messages in the S1 protocol.

FIG. 3 is a schematic of a protocol stack of X2 protocols. As shown inFIG. 3, the protocol stack of X2 protocols has a configuration similarto that of the protocol stack of S1 protocols, and the descriptionsthereof are omitted. The X2 application software in the top applicationlayer sets an SCTP link (inter-station link) to that of another wirelessbase station, thereby communicating with the wireless base stationhaving the inter-station link by using messages in an X2 protocol. As aresult, after setting such an inter-station link in the X2 protocol, thewireless base station X performs handover directly with the wirelessbase station Y by using messages in the X2 protocol.

Referring to FIGS. 4 and 5, the following briefly describes a procedureof S1 handover using an inter-station link in the S1 protocol, and aprocedure of X2 handover using an inter-station link in the X2 protocol.The S1 handover refers to handover using an inter-station link in the S1protocol, and X2 handover refers to handover using an inter-station linkin the X2 protocol. Suppose that a mobile communication terminalperforming wireless communication with the wireless base station X movesinto a control region of the wireless base station Y.

FIG. 4 is a simplified sequence diagram depicting a procedure of S1handover performed when no inter-station link in the X2 protocol hasbeen set. As shown in FIG. 4, when a mobile communication terminal movesfrom a control region of the wireless base station X into a controlregion of the wireless base station Y, the mobile communication terminaltransmits a handover (HO) request to the wireless base station X withwhich the mobile communication terminal is in wireless communication.Because no inter-station link in the X2 protocol has been set to thewireless base station Y, the wireless base station X cannot use X2handover, and thus transmits the handover request to the wireless basestation Y through the EPC. Receiving the handover request, the wirelessbase station Y establishes a wireless path to the EPC, and transmits aresponse to the handover request to the wireless base station X throughthe EPC. Receiving the response to the handover request, the wirelessbase station X transmits a handover command to the mobile communicationterminal. The mobile communication terminal establishes a wireless pathto the wireless base station Y, and transmits a movement notification tothe destination, i.e., the wireless base station Y. Receiving themovement notification, the wireless base station Y transmits to the EPCa path switch request to switch the wired path of the mobilecommunication terminal, from a wired path via the wireless base stationX to a wired path via the wireless base station Y. Receiving the pathswitch request, the EPC switches the wired path via the wireless basestation X to the wired path via the wireless base station Y, and thentransmits a path switch response to the wireless base station Y.Receiving the path switch response, the wireless base station Ytransmits a command to release resources to the wireless base station Xthrough the EPC. The wireless base station X releases the resources usedto perform wireless communication with the mobile communicationterminal, and S1 handover is terminated.

FIG. 5 is a simplified sequence diagram depicting a procedure of X2handover performed when an inter-station link in the X2 protocol hasbeen set. In FIG. 5, an inter-station link in the X2 protocol is setbetween the wireless base stations X and Y. As shown in FIG. 5, when amobile communication terminal moves from a control region of thewireless base station X into a control region of the wireless basestation Y, the mobile communication terminal transmits a handover (HO)request to the wireless base station X with which the mobilecommunication terminal is in wireless communication. Because theinter-station link in the X2 protocol has been set to the wireless basestation Y, the wireless base station X transmits the handover request tothe wireless base station Y. Receiving the handover request, thewireless base station Y establishes a wireless path to the wireless basestation X, and transmits a response to the handover request thereto.Receiving the response to the handover request, the wireless basestation X transmits a handover command to the mobile communicationterminal. The mobile communication terminal establishes a wireless pathto the wireless base station Y, and transmits a movement notification tothe destination, i.e., the wireless base station Y. Receiving themovement notification, the wireless base station Y transmits to the EPCa path switch request to switch the wired path of the mobilecommunication terminal, from a wired path via the wireless base stationX to a wired path via the wireless base station Y. Receiving the pathswitch request, the EPC switches the wired path via the wireless basestation X to the wired path via the wireless base station Y, and thentransmits a path switch response to the wireless base station Y.Receiving the path switch response, the wireless base station Ytransmits a command to release resources to the wireless base station X.The wireless base station X releases the resources used to performwireless communication with the mobile communication terminal, and X2handover is terminated.

As to the number of times of transmission and reception to and from theEPC, the procedure of X2 handover is about ¼ the procedure of S1handover. Thus, when many mobile communication terminals switch theircommunication recipient from the wireless base station X to the wirelessbase station Y, the processing load on the EPC can be reduced in X2handover more than in S1 handover.

FIG. 6 is a functional block diagram of the entire communication controlsystem according to the first embodiment. As shown in FIG. 6, acommunication control system 1 includes a wireless base station X 10, anEPC 20, a wireless base station Y 30, and a mobile communicationterminal 40.

The wireless base station X 10 includes a wireless transmitting andreceiving unit 100, a call control unit 110, a wired transmitting andreceiving unit 120, a link control determining unit 130, aninter-station link control unit 140, and wireless base stationinformation 150, and handover execution information 160.

The wireless transmitting and receiving unit 100 transmits and receivesa control signal to and from the mobile communication terminal 40.Specifically, the wireless transmitting and receiving unit 100 receivesa handover request, transmitted from the mobile communication terminal40 and made to the wireless base station Y 30, and then outputs thehandover request to a handover type determining section 111. Thewireless transmitting and receiving unit 100 also receives a handoverresponse to the handover request from a handover responding section 114,and transmits the handover response to the mobile communication terminal40.

The call control unit 110 controls calls of each mobile communicationterminal, depending on a message received from the wireless base stationY 30, the EPC 20, or the mobile communication terminal 40. The callcontrol unit 110 includes the handover type determining section 111, ahandover requesting section 112, and the handover responding section114.

The handover type determining section 111 acquires from the wirelesstransmitting and receiving unit 100 a handover request made to thewireless base station Y 30, so as to determine whether an inter-stationlink in an X2 protocol (hereinafter, “inter-station link”) has been setto the wireless base station Y 30. Specifically, the handover typedetermining section 111 refers to an inter-station setting state storedin the wireless base station information 150 and indicating whether aninter-station link has been set to each wireless base station, so as todetermine whether the inter-station link has been set to the wirelessbase station Y 30. If no inter-station link has been set to the wirelessbase station Y 30, the handover type determining section 111 attempts torequest the wireless base station Y 30 through the EPC 20, for thesetting information necessary for setting the inter-station link. Thus,the handover type determining section 111 outputs to the handoverrequesting section 112 a notification that a wireless base stationnumber and inter-station link setting information of the wireless basestation Y 30 are requested. On the contrary, if an inter-station linkhas been set to the wireless base station Y 30, the handover typedetermining section 111 has no need to request the wireless base stationY 30 for the setting information necessary for setting the inter-stationlink. Thus, the handover type determining section 111 outputs to thehandover requesting section 112 a notification that the wireless basestation number and the inter-station link setting information of thewireless base station Y 30 are not requested.

When acquiring, from the handover type determining section 111, thenotification that the wireless base station number and the inter-stationlink setting information of the wireless base station Y 30 arerequested, the handover requesting section 112 outputs, to the wiredtransmitting and receiving unit 120, a handover request that requestsswitching of the wireless path using S1 handover and that includes arequest for the inter-station link setting information of the wirelessbase station Y 30 (hereinafter, “S1 handover request”). On the contrary,when acquiring, from the handover type determining section 111, thenotification that the wireless base station number and the inter-stationlink setting information of the wireless base station Y 30 are notrequested, the handover requesting section 112 outputs to the wiredtransmitting and receiving unit 120 a handover request that requestsswitching of the wired path using X2 handover and that includesinformation indicating that the request for the inter-station linksetting information of the wireless base station Y 30 is not required(hereinafter, “X2 handover request”).

The handover responding section 114 acquires a handover response fromthe wired transmitting and receiving unit 120, and outputs theinter-station link setting information of the wireless base station Y30, included in the handover response, to a setting informationacquiring section 131. The handover responding section 114 also acquiresa request to switch the wired path of the mobile communication terminal40 (path switch request) from the wired transmitting and receiving unit120. In this case, the handover responding section 114 switches thewired path of the mobile communication terminal 40 from a wired path viathe current wireless base station X 10 to a wired path via the wirelessbase station Y 30, and terminates the handover. The handover respondingsection 114 then outputs to a handover termination acquiring section 132a handover termination notification including: the wireless base stationnumber of the wireless base station Y 30; and information indicatingwhether either S1 handover or X2 handover has been performed.

The wired transmitting and receiving unit 120 transmits and receives acontrol signal to and from the EPC 20 and a neighboring wireless basestation. Specifically, when acquiring an S1 handover request from thehandover requesting section 112, the wired transmitting and receivingunit 120 transmits the S1 handover request to the EPC 20. On thecontrary, when acquiring an X2 handover request from the handoverrequesting section 112, the wired transmitting and receiving unit 120transmits the X2 handover request to the wireless base station Y 30.Further, when receiving a handover response from the EPC 20 or thewireless base station Y 30, the wired transmitting and receiving unit120 outputs the received handover response to the handover respondingsection 114. The wired transmitting and receiving unit 120 also outputsa path switch request, received from the EPC 20 or the wireless basestation Y 30, to the handover responding section 114. Further, whenacquiring an SCTP link setting request made to the wireless base stationY 30 from a setting requesting section 141, the wired transmitting andreceiving unit 120 transmits the SCTP link setting request to thewireless base station Y 30. The wired transmitting and receiving unit120 then receives an SCTP link setting response to the SCTP link settingrequest from the wireless base station Y 30, and outputs the SCTP linksetting response to a setting responding section 142.

The link control determining unit 130 acquires the inter-station linksetting information of the wireless base station Y 30, to establish alink to the wireless base station Y 30. The link control determiningunit 130 then determines whether to make a request to set theinter-station link to the wireless base station Y 30. The link controldetermining unit 130 includes the setting information acquiring section131, a setting request determining section 133, and the handovertermination acquiring section 132.

Acquiring the inter-station link setting information of the wirelessbase station Y 30 from the handover responding section 114, the settinginformation acquiring section 131 stores the acquired inter-station linksetting information of the wireless base station Y 30, in the wirelessbase station information 150. Examples of the inter-station link settinginformation of the wireless base station Y 30 include an IP address anda port number of the wireless base station Y 30.

Acquiring the handover termination notification made to the wirelessbase station Y 30 from the handover responding section 114, the handovertermination acquiring section 132 increments by one the number ofhandovers (S1 or X2) made to the wireless base station number of thewireless base station Y 30, and stores the incremented number in thehandover execution information 160. The handover termination acquiringsection 132 then outputs an inter-station link setting request commandmade to the wireless base station Y 30 to the setting requestdetermining section 133.

The setting request determining section 133 acquires, from the handovertermination acquiring section 132, the inter-station link settingrequest command made to the wireless base station Y 30. If the receivedrequest command matches the conditions for a request to set theinter-station link, the setting request determining section 133 outputsa request to set the inter-station link to the wireless base station Y30 (i.e., inter-station link setting request) to the setting requestingsection 141. Specifically, the setting request determining section 133refers to the inter-station setting state stored in the wireless basestation information 150 and indicating whether the inter-station linkhas been set to the wireless base station Y 30, so as to determinewhether the inter-station link has been set to the wireless base stationY 30. If no inter-station link has been set to the wireless base stationY 30, the setting request determining section 133 refers to the handoverexecution information 160 and acquires the number of S1 handovers madeto the wireless base station Y 30, so as to determine whether the numberof the performed S1 handovers is equal to or greater than apredetermined number. The predetermined number is a number indicatinghow many times S1 handover is performed within a certain period of timeand expected to trigger the processing load on the EPC 20 to exceed apredetermined reference value. The predetermined number is, for example,10 per hour. If the number of performed handovers is equal to or greaterthan the predetermined number, the setting request determining section133 outputs the inter-station link setting request made to the wirelessbase station Y 30 to the setting requesting section 141. In theforegoing, the setting request determining section 133 determinesmatching of the inter-station link setting request upon acquiring theinter-station link setting request command from the handover terminationacquiring section 132. The setting request determining section 133 isnot limited to this, and may make the determination regularly orirregularly.

The inter-station link control unit 140 manages an inter-station link toa neighboring wireless base station, inputs and outputs messages forsetting an inter-station link, and sets an inter-station link. Theinter-station link control unit 140 includes the setting requestingsection 141 and the setting responding section 142.

The setting requesting section 141 acquires the inter-station linksetting request made to the wireless base station Y 30 from the settingrequest determining section 133. The setting requesting section 141 thenoutputs an SCTP link setting request made to the wireless base station Y30 to the wired transmitting and receiving unit 120. The inter-stationlink setting request includes an IP address of the wireless base stationX 10, and a port number used to set an inter-station link to thewireless base station Y 30.

The setting responding section 142 acquires, from the wired transmittingand receiving unit 120, an SCTP link setting response from the wirelessbase station Y 30, and then stores information indicating that theinter-station link has been set to the wireless base station Y 30, inthe wireless base station information 150.

The wireless base station information 150 stores therein theinter-station setting state of the wireless base station Y 30neighboring the current wireless base station X 10, and settinginformation necessary for setting an inter-station link. Referring toFIG. 7, the following describes a data structure of the wireless basestation information 150. As shown in FIG. 7, the wireless base stationinformation 150 stores therein sets of information including: a wirelessbase station number uniquely identifying a wireless base stationneighboring the current wireless base station; the inter-station linksetting state; an IP address; and a port number, in a manner that thesets of information are associated with respective wireless base stationnumbers. The inter-station link setting state indicates whether aninter-station link has been set to the current wireless base station.For example, as the inter-station link setting state, “set” is held whenthe inter-station link has been set, while “unset” is held when nointer-station link has been set. The IP address is an IP address of awireless base station corresponding to a wireless base station number.The port number is the number of a port used by a wireless base stationcorresponding to a wireless base station number to set an inter-stationlink to the current wireless base station.

Referring back to FIG. 6, the handover execution information 160 storestherein the number of handovers of each type (S1 or X2) made by themobile communication terminal 40 from the current wireless base stationX 10 to its neighboring wireless base station Y 30. Referring to FIG. 8,the following describes an example of a data structure of the handoverexecution information 160. As shown in FIG. 8, the handover executioninformation 160 stores therein sets of information including: a wirelessbase station number uniquely identifying a neighboring wireless basestation; the number of performed S1 handovers; and the number ofperformed X2 handovers, in a manner that the sets of information areassociated with respective wireless base station numbers. The number ofperformed S1 handovers and the number of performed X2 handovers storedin the handover execution information 160 are updated to zero everypredetermined period of time. This allows the setting requestdetermining section 133 to determine an execution frequency of S1handovers and an execution frequency of X2 handovers every predeterminedperiod of time. Thus, an inter-station link can be set according to theever-changing processing load on the EPC 20. The predetermined period oftime may be, for example, one hour or one day.

The wireless base station Y 30 includes a wireless transmitting andreceiving unit 300, a call control unit 310, a wired transmitting andreceiving unit 320, an inter-station link control unit 340, and aninter-station setting information 370.

The wireless transmitting and receiving unit 300 transmits and receivesa control signal to and from the mobile communication terminal 40.Specifically, the wireless transmitting and receiving unit 300 receivesa handover completion notification from the mobile communicationterminal 40, and outputs the handover completion notification to ahandover responding section 314.

The call control unit 310 controls calls of each mobile communicationterminal, depending on a message received from the wireless base stationY 30, the EPC 20, or the mobile communication terminal 40. The callcontrol unit 310 includes the handover responding section 314.

When acquiring an S1 handover request including a request forinter-station link setting information from the wired transmitting andreceiving unit 320, the handover responding section 314 refers to theinter-station setting information 370 and acquires inter-station linksetting information (an IP address and a port number) of the currentwireless base station. The handover responding section 314 then createsa handover response including the acquired inter-link settinginformation, and outputs the handover response to the wired transmittingand receiving unit 320. On the other hand, when acquiring, from thewired transmitting and receiving unit 320, an X2 handover requestincluding information indicating that the request for inter-station linksetting information is not required, the handover responding section 314outputs a handover response not including the inter-station link settinginformation to the wired transmitting and receiving unit 320.

The wired transmitting and receiving unit 320 transmits and receives acontrol signal to and from the EPC 20 and a neighboring wireless basestation. Specifically, when acquiring a handover request from the EPC 20or the wireless base station X 10, the wired transmitting and receivingunit 320 outputs the handover request to the handover responding section314. On the contrary, when acquiring a handover response including theinter-station link setting information from the handover respondingsection 314, the wired transmitting and receiving unit 320 transmits thehandover response to the EPC 20. Further, when acquiring an SCTP linksetting request made to the current wireless base station Y 30 from thewireless base station X 10, the wired transmitting and receiving unit320 outputs the SCTP link setting request to a setting respondingsection 342 to establish a link to the wireless base station X 10. Onthe contrary, when acquiring an SCTP link setting response to the SCTPlink setting request from the setting responding section 342, the wiredtransmitting and receiving unit 320 transmits the SCTP link settingresponse to the wireless base station X 10.

The inter-station link control unit 340 manages an inter-station link toa neighboring wireless base station, and inputs and outputs a signal forsetting the inter-station link. The inter-station link control unit 340includes the setting responding section 342.

The setting responding section 342 acquires an SCTP link setting requestfrom the wired transmitting and receiving unit 320, sets aninter-station link to the wireless base station X 10, and outputs anSCTP link setting response to the wired transmitting and receiving unit320.

Referring to FIGS. 9 and 10, the following describes an entire processsequence performed by the communication control system according to thefirst embodiment. FIG. 9 depicts a handover procedure performed by thecommunication control system, and FIG. 10 depicts a procedure forsetting an inter-station link. The mobile communication terminal 40 isin wireless communication with the wireless base station X 10. Thewireless base station X 10 has no inter-station link in the X2 protocolto the wireless base station Y 30.

FIG. 9 depicts a sequence of a handover procedure performed by thecommunication control system according to the first embodiment.

When a user moves geographically for example, and enters a controlregion of the wireless base station Y 30, a trigger for handover occursin the mobile communication terminal 40 (S101). The mobile communicationterminal 40 then transmits a handover request to the wireless basestation X 10 (S102).

Receiving the handover request, the wireless transmitting and receivingunit 100 of the wireless base station X 10 outputs the handover requestto the handover type determining section 111 of the call control unit110 (S103).

The handover type determining section 111 of the call control unit 110refers to the inter-station setting state stored in the wireless basestation information 150, so as to determine whether an inter-stationlink has been set to the wireless base station Y 30. If no inter-stationlink has been set to the wireless base station Y 30, the handover typedetermining section 111 transmits a handover request including a requestfor the setting information necessary for setting an inter-station linkto the wireless base station Y 30, to the EPC 20 through the wiredtransmitting and receiving unit 120 (S104 to S105).

Receiving the handover request from the wireless base station X 10, theEPC 20 transmits the handover request to the wireless base station Y 30(S106). Receiving the handover request from the EPC 20, the wiredtransmitting and receiving unit 320 of the wireless base station Y 30outputs the handover request to the handover responding section 314 ofthe call control unit 310 (S107). Receiving the handover request, thehandover responding section 314 acquires the inter-station link settinginformation of the current wireless base station according to therequest for the setting information necessary for setting aninter-station link to the current wireless base station, included in thehandover request. The handover responding section 314 then transmits thehandover response including the acquired setting information to the EPC20 through the wired transmitting and receiving unit 320 (S108 to S109).

Receiving the handover response from the wireless base station Y 30, theEPC 20 transmits the handover response to the wireless base station X 10(S110). Receiving the handover response from the EPC 20, the wiredtransmitting and receiving unit 120 of the wireless base station X 10outputs the handover response to the handover responding section 114 ofthe call control unit 110 (S111). The handover responding section 114outputs the handover response to the setting information acquiringsection 131 of the link control determining unit 130 (S113), whiletransmitting the handover response to the mobile communication terminal40 through the wireless transmitting and receiving unit 100 (S112 andS114). The setting information acquiring section 131 stores theinter-station link setting information (an IP address and a port number)of the wireless base station Y 30, included in the handover response, inthe wireless base station information 150.

Receiving the handover response from the wireless base station X 10, themobile communication terminal 40 establishes a wireless path to thewireless base station Y 30, and transmits a handover completionnotification to the wireless base station Y 30 (S115). Receiving thehandover completion notification from the mobile communication terminal40, the wireless transmitting and receiving unit 300 of the wirelessbase station Y 30 outputs the handover completion notification to thehandover responding section 314 of the call control unit 310 (S116).Acquiring the handover completion notification, the handover respondingsection 314 transmits a path switch request to the EPC 20 through thewired transmitting and receiving unit 320 (S117 to S118).

Receiving the path switch request from the wireless base station Y 30,the EPC 20 establishes a wired path to the wireless base station Y 30,and transmits a path switch response to the wireless base station Y 30(S119).

Receiving the path switch response from the EPC 20, the wiredtransmitting and receiving unit 320 of the wireless base station Y 30outputs the path switch response to the handover responding section 314of the call control unit 310 (S120). Acquiring the path switch response,the handover responding section 314 transmits the path switch requestmade to the wireless base station X 10, to the EPC 20 through the wiredtransmitting and receiving unit 320 (S121 to S122).

Receiving the path switch request from the wireless base station Y 30,the EPC 20 transmits the path switch request to the wireless basestation X 10 (S123). Receiving the path switch request from the EPC 20,the wired transmitting and receiving unit 120 of the wireless basestation X 10 outputs the path switch request to the handover respondingsection 114 of the call control unit 110 (S124). Acquiring the pathswitch request, the handover responding section 114 switches the path,and outputs a handover termination notification to the link controldetermining unit 130 (S125). Acquiring the handover terminationnotification from the handover responding section 114, the handovertermination acquiring section 132 of the link control determining unit130 increments the number of performed S1 handovers by one, and storesthe incremented number in the handover execution information 160.

FIG. 10 depicts a sequence of a process for setting an inter-stationlink in the communication control system according to the firstembodiment. Such an inter-station link setting process is started astriggered by activating the inter-station link setting request commandat a predetermined time.

Acquiring the inter-station link setting request command made to thewireless base station Y 30, the setting request determining section 133performs the process for determining an inter-station link settingrequest (S126). In other words, the setting request determining section133 determines whether an inter-station link has been set to thewireless base station Y 30. If no inter-station link has been set to thewireless base station Y 30, the setting request determining section 133determines whether the number of S1 handovers made to the wireless basestation Y 30 is equal to or greater than a predetermined number. If thenumber of performed S1 handovers is equal to or greater than thepredetermined number, the setting request determining section 133outputs an inter-station link setting request to the setting requestingsection 141 of the inter-station link control unit 140 (S127).

Acquiring the inter-station link setting request from the settingrequest determining section 133, the setting requesting section 141 ofthe inter-station link control unit 140 transmits an SCTP link settingrequest to the wireless base station Y 30 through the wired transmittingand receiving unit 120 (S128 to S129).

Acquiring the SCTP link setting request from the wireless base station X10, the wired transmitting and receiving unit 320 of the wireless basestation Y 30 outputs the SCTP link setting request to the settingresponding section 342 of the inter-station link control unit 340(S130). Acquiring the SCTP link setting request from the wiredtransmitting and receiving unit 320, the setting responding section 342sets an inter-station link to the wireless base station X 10, andoutputs an SCTP link setting response to the wired transmitting andreceiving unit 320 (S131). Acquiring the SCTP link setting response fromthe setting responding section 342, the wired transmitting and receivingunit 320 transmits the SCTP link setting response to the wireless basestation X 10 (S132).

Acquiring the SCTP link setting response from the wireless base stationY 30, the wired transmitting and receiving unit 120 of the wireless basestation X 10 outputs the SCTP link setting response to the settingresponding section 142 of the inter-station link control unit 140(S133). Acquiring the SCTP link setting response from the wiredtransmitting and receiving unit 120, the setting responding section 142updates the inter-station link setting state of the wireless basestation Y 30 from “unset” to “set” in the wireless base stationinformation 150.

The forgoing describes the inter-station link setting process as beingstarted by activating the inter-station link setting request command ata predetermined time. The inter-station link setting process is notlimited to this, and may be started when the handover terminationacquiring section 132 outputs the inter-station link setting requestcommand, or may be started when the inter-station link setting requestcommand is made irregularly. Further, the foregoing describes theinter-station link setting process performed only on the wireless basestation Y 30. The inter-station link setting process is not limited tothis, and may be performed on all wireless base stations stored in thewireless base station information 150.

Referring to FIG. 11, the following describes the process fordetermining an inter-station link setting request according to the firstembodiment. FIG. 11 is a flowchart of the process for determining aninter-station link setting request according to the first embodiment.The process for determining an inter-station link setting request isperformed only on the wireless base station Y 30.

Acquiring the inter-station link setting request command for setting aninter-station link to the wireless base station Y 30, the settingrequest determining section 133 determines whether an inter-station linkhas been set to the wireless base station Y 30 (S201). Specifically, thesetting request determining section 133 refers to the inter-station linksetting information of the wireless base station Y 30 stored in thewireless base station information 150, so as to determine whether theinter-station link setting information indicates “set” or “unset”.

If the inter-station link setting state of the wireless base station Y30 is “set” (YES at S201), the setting request determining section 133determines that setting of an inter-station link is “not required”(S202). Because the link has been established to the wireless basestation Y 30, the setting request determining section 133 terminates theprocess for determining an inter-station link setting request.

On the contrary, if the inter-station link setting state of the wirelessbase station Y 30 is not “set” (NO at S201), the setting requestdetermining section 133 determines whether the number of S1 handoversmade to the wireless base station Y 30 is equal to or greater than apredetermined number (S203). Specifically, the setting requestdetermining section 133 refers to the number of S1 handovers made to thewireless base station Y 30 stored in the handover execution information160, so as to determine whether the number of performed S1 handovers isequal to or greater than a predetermined number, for example, 10.

When the number of performed S1 handovers is less than ten (NO at S203),the setting request determining section 133 determines that setting ofan inter-station link is “not required” (S202). Because S1 handover isnot performed frequently and thus no processing load is imposed on theEPC 20, the setting request determining section 133 terminates theprocess for determining an inter-station link setting request.

On the contrary, if the number of performed S1 handovers is equal to orgreater than ten (YES at S203), the setting request determining section133 determines that setting of an inter-station link is “required”(S204), and terminates the process for determining an inter-station linksetting request.

When setting of an inter-station link is “required”, the setting requestdetermining section 133 outputs an inter-station link setting requestmade to the wireless base station Y 30 to the setting requesting section141. The setting requesting section 141 outputs the inter-station linksetting request to set an inter-station link to the wireless basestation Y 30, to the wireless base station Y 30 through the wiredtransmitting and receiving unit 120. Accordingly, the wireless basestation Y 30 sets the inter-station link.

In this way, the wireless base station X 10 can establish the link tothe wireless base station Y 30, and thus can make the next handover tothe wireless base station Y 30 using X2 handover, not S1 handover. Thisreduces the processing load on the EPC 20. Further, if the number ofperformed S1 handovers is less than a predetermined number, the wirelessbase station X 10 does not establish a link to the wireless base stationY 30, thus allowing the wireless base station X 10 not to use resourcesnecessary for setting an inter-station link. This enables efficient useof the resources allocated to the inter-station link.

According to the first embodiment, when the mobile communicationterminal 40 makes a request to switch a communication recipient from thewireless base station X 10 to the wireless base station Y 30, thewireless base station X 10 determines whether an inter-station link hasbeen set to the wireless base station Y 30. As a result, if nointer-station link has been set to the wireless base station Y 30, thewireless base station X 10 acquires the setting information necessaryfor setting an inter-station link to the wireless base station Y 30,from the wireless base station Y 30 through the EPC 20. Based on theacquired setting information of the wireless base station Y 30, thewireless base station X 10 requests the wireless base station Y 30 toset an inter-station link thereto.

In this way, after the direct link is set to the wireless base station Y30, the wireless base station X 10 can perform switching of the wirelesspath directly with the wireless base station Y 30. Thus, when the mobilecommunication terminal 40 makes a request to switch a communicationrecipient from the wireless base station X 10 to the wireless basestation Y 30, the wireless base station X 10 can perform the switchingdirectly, not through the EPC 20 that is located between the wirelessbase stations X 10 and Y 30 and plays a part in, for example, switchingprocess. This reduces the processing load on the EPC 20.

Second Embodiment

In the first embodiment, when a mobile communication terminal makes anS1 handover from a wireless base station being in wireless communicationto a neighboring wireless base station having no inter-station link inthe X2 protocol to the wireless base station, the wireless base stationrequests the neighboring wireless base station to set an inter-stationlink in the X2 protocol. The present invention is not limited to this,and after an inter-station link in the X2 protocol is set between thewireless base station and the neighboring wireless base station, thewireless base station may determine the execution state of X2 handover,so as to request the neighboring wireless base station to remove theinter-station link.

In a second embodiment of the present invention, after an inter-stationlink in the X2 protocol is set between a wireless base station and aneighboring wireless base station, the wireless base station determinesthe execution state of X2 handover, so as to request the neighboringwireless base station to remove the inter-station link.

Referring to FIG. 12, the following describes an entire structure of acommunication control system according to the second embodiment. FIG. 12is a functional block diagram of an entire communication control systemaccording to the second embodiment. As shown in FIG. 12, a communicationcontrol system 2 according to the second embodiment includes a removalrequest determining section 533, a removal requesting section 541, aremoval responding section 542, and a removal responding section 642, inaddition to the elements of the communication control system 1 accordingto the first embodiment (shown in FIG. 6). In FIG. 12, elements beingthe same as those shown in FIG. 6 are indicated by the same referencenumerals, and the detailed descriptions thereof are omitted.

The handover termination acquiring section 132 acquires a handovertermination notification made to the wireless base station Y 30 from thehandover responding section 114, and then outputs an inter-station linkremoval request command made to the wireless base station Y 30 to theremoval request determining section 533.

The removal request determining section 533 acquires the inter-stationlink removal request command made to the wireless base station Y 30 fromthe handover termination acquiring section 132. If the inter-stationlink removal request command matches the conditions for requestingremoval of the inter-station link, the removal request determiningsection 533 outputs the inter-station link removal request made to thewireless base station Y 30 to the removal requesting section 541.Specifically, the removal request determining section 533 refers to theinter-station setting state stored in the wireless base stationinformation 150 and indicating whether an inter-station link has beenset to the wireless base station Y 30, so as to determine whether aninter-station link has been set to the wireless base station Y 30. If aninter-station link has been set to the wireless base station Y 30, theremoval request determining section 533 refers to the handover executioninformation 160 and acquires the number of X2 handovers made to thewireless base station Y 30, so as to determine whether the number ofperformed X2 handovers is equal to or less than a predetermined number.The predetermined number is the number of X2 handovers performed withina certain period of time and expected to impose no processing load atall on the EPC 20 even if the performed X2 handovers include S1handovers. The predetermined number is, for example, 2 per hour. Whenthe number of the performed handovers is equal to or less than thepredetermined number, the removal request determining section 533outputs an inter-station link setting request made to the wireless basestation Y 30 to the removal requesting section 541. In the foregoing,the removal request determining section 533 determines the inter-stationlink removal request when acquiring the inter-station link removalrequest command from the handover termination acquiring section 132. Theremoval request determining section 533 is not limited to this, and maymake the determination regularly or irregularly.

The removal requesting section 541 acquires from the removal requestdetermining section 533 the inter-station link removal request made tothe wireless base station Y 30, and then outputs an SCTP link removalrequest made to the wireless base station Y 30 to the wired transmittingand receiving unit 120. The inter-station link removal request includesan IP address of the current wireless base station X 10, and a portnumber used to set an inter-station link to the wireless base station Y30.

The removal responding section 542 acquires an SCTP link removalresponse made to the wireless base station Y 30 from the wiredtransmitting and receiving unit 120, and then stores informationindicating that the inter-station link to the wireless base station Y 30has been removed, in the wireless base station information 150.

The removal responding section 642 acquires the SCTP link removalrequest from the wired transmitting and receiving unit 320, removes theinter-station link to the wireless base station X 10, and outputs anSCTP link removal response to the wired transmitting and receiving unit320.

The wired transmitting and receiving unit 120 acquires the SCTP linkremoval request made to the wireless base station Y 30 from the removalrequesting section 541, and then transmits the SCTP link removal requestto the wireless base station Y 30. Further, the wired transmitting andreceiving unit 120 receives the SCTP link removal response to the SCTPlink removal request from the wireless base station Y 30, and outputsthe SCTP link removal response to the removal responding section 542.

The wired transmitting and receiving unit 320 receives the SCTP linkremoval request made to the current wireless base station from thewireless base station X 10, and then outputs the SCTP link removalrequest to the removal responding section 642 to cancel the link to thewireless base station X 10. Further, the wired transmitting andreceiving unit 320 acquires an SCTP link removal response to the SCTPlink removal request from the removal responding section 642, andtransmits the SCTP link removal response to the wireless base station X10.

Referring to FIGS. 13 and 14, the following describes an entire processsequence performed by the communication control system according to thesecond embodiment. FIG. 13 depicts a handover procedure performed by thecommunication control system, and FIG. 14 depicts a procedure forremoving an inter-station link. The mobile communication terminal 40 isin wireless communication with the wireless base station X 10. Further,the wireless base station X 10 has an inter-station link in the X2protocol to the wireless base station Y 30.

FIG. 13 depicts a sequence of a handover procedure performed by thecommunication control system according to the second embodiment.

When a user moves geographically for example, and enters a controlregion of the wireless base station Y 30, a trigger for handover occursin the mobile communication terminal 40 (S301). The mobile communicationterminal 40 then transmits a handover request to the wireless basestation X 10 (S302).

Receiving the handover request, the wireless transmitting and receivingunit 100 of the wireless base station X 10 outputs the handover requestto the handover type determining section 111 of the call control unit110 (S303).

The handover type determining section 111 of the call control unit 110refers to the inter-station setting state stored in the wireless basestation information 150, so as to determine whether an inter-stationlink has been set to the wireless base station Y 30. When aninter-station link has been set to the wireless base station Y 30, thehandover type determining section 111 has already acquired the settinginformation necessary for setting the inter-station link. Thus, thehandover type determining section 111 transmits a handover requestincluding information indicating that a request for the settinginformation necessary for setting the inter-station link is notrequired, to the wireless base station Y 30 through the wiredtransmitting and receiving unit 120 (S304 to S305).

Receiving the handover request from the wireless base station X 10, thewired transmitting and receiving unit 320 of the wireless base station Y30 outputs the handover request to the handover responding section 314of the call control unit 310 (S306). Because the request for theinter-station link setting information is not required, the handoverresponding section 314 transmits a handover response not including theinter-station link setting information, to the wireless base station X10 through the wired transmitting and receiving unit 320 (S307 to S308).

Receiving the handover response from the wireless base station Y 30, thewired transmitting and receiving unit 120 of the wireless base station X10 outputs the handover response to the handover responding section 114of the call control unit 110 (S309). The handover responding section 114outputs the handover response to the setting information acquiringsection 131 of the link control determining unit 530 (S311), whiletransmitting the handover response to the mobile communication terminal40 through the wireless transmitting and receiving unit 100 (S310 andS312). The setting information acquiring section 131 performs no processbecause the handover response does not include the setting informationfor setting the inter-station link to the wireless base station Y 30.

Receiving the handover response from the wireless base station X 10, themobile communication terminal 40 establishes a wireless path to thewireless base station Y 30, and transmits a handover completionnotification to the wireless base station Y 30 (S313). Receiving thehandover completion notification from the mobile communication terminal40, the wireless transmitting and receiving unit 300 of the wirelessbase station Y 30 outputs the handover completion notification to thehandover responding section 314 of the call control unit 310 (S314).Acquiring the handover completion notification, the handover respondingsection 314 transmits a path switch request to the EPC 20 through thewired transmitting and receiving unit 320 (S315 to S316).

Receiving the path switch request from the wireless base station Y 30,the EPC 20 establishes a wired path to the wireless base station Y 30,and transmits a path switch response to the wireless base station Y 30(S317). Receiving the path switch response from the EPC 20, the wiredtransmitting and receiving unit 320 of the wireless base station Y 30outputs the path switch response to the handover responding section 314of the call control unit 310 (S318). Acquiring the path switch response,the handover responding section 314 transmits a path switch request madeto the wireless base station X 10, to the wireless base station X 10through the wired transmitting and receiving unit 320 (S319 to S320).

Receiving the path switch request from the wireless base station Y 30,the wired transmitting and receiving unit 120 of the wireless basestation X 10 outputs the path switch request to the handover respondingsection 114 of the call control unit 110 (S321). Acquiring the pathswitch request, the handover responding section 114 switches the path,and outputs a handover termination notification to a link controldetermining unit 530 (S322). Acquiring the handover terminationnotification from the handover responding section 114, the handovertermination acquiring section 132 of the link control determining unit530 increments the number of performed X2 handovers by one, and storesthe incremented number in the handover execution information 160.

FIG. 14 depicts a sequence of an inter-station link removal process inthe communication control system according to the second embodiment. Theinter-station link removal process is started as triggered by activatingthe inter-station link removal request command at a predetermined time.

Acquiring the inter-station link removal request command made to thewireless base station Y 30, the removal request determining section 533determines an inter-station link removal request (S323). In other words,the removal request determining section 533 determines whether aninter-station link has been set to the wireless base station Y 30. If aninter-station link has been set to the wireless base station Y 30, theremoval request determining section 533 determines whether the number ofX2 handovers made to the wireless base station Y 30 is equal to or lessthan a predetermined number. If the number of the performed X2 handoversis equal to or less than the predetermined number, the removal requestdetermining section 533 outputs the inter-station link removal requestto the removal requesting section 541 of an inter-station link controlunit 540 (S324).

Acquiring the inter-station link removal request from the removalrequest determining section 533, the removal requesting section 541 ofthe inter-station link control unit 540 transmits an SCTP link removalrequest to the wireless base station Y 30 through the wired transmittingand receiving unit 120 (S325 to S326).

Acquiring the SCTP link removal request from the wireless base station X10, the wired transmitting and receiving unit 320 of the wireless basestation Y 30 outputs the SCTP link removal request to the removalresponding section 642 of an inter-station link control unit 640 (S327).Acquiring the SCTP link removal request from the wired transmitting andreceiving unit 320, the removal responding section 642 removes theinter-station link to the wireless base station X 10, and outputs anSCTP link removal response to the wired transmitting and receiving unit320 (S328). Acquiring the SCTP link removal response from the removalresponding section 642, the wired transmitting and receiving unit 320transmits the SCTP link removal response to the wireless base station X10 (S329).

Acquiring the SCTP link setting response from the wireless base stationY 30, the wired transmitting and receiving unit 120 of the wireless basestation X 10 outputs the SCTP link removal response to the removalresponding section 542 of the inter-station link control unit 540(S330). The removal responding section 542 acquires the SCTP linkremoval response from the wired transmitting and receiving unit 120, andupdates the inter-station setting state of the wireless base station Y30 from “set” to “unset” in the wireless base station information 150.

The forgoing describes the inter-station link removal process as beingstarted by activating the inter-station link removal request command ata predetermined time. The inter-station link removal process is notlimited to this, and may be started when the handover terminationacquiring section 132 outputs the inter-station link removal requestcommand, or may be started when the inter-station link removal requestcommand is made irregularly. Further, the foregoing describes theinter-station link removal process performed only on the wireless basestation Y 30. The inter-station link setting process is not limited tothis, and may be performed on all wireless base stations stored in thewireless base station information 150.

Referring to FIG. 15, the following describes the process fordetermining an inter-station link removal request according to thesecond embodiment. FIG. 15 is a flowchart of the process for determiningan inter-station link removal request according to the secondembodiment. The process for determining an inter-station link removalrequest is performed only on the wireless base station Y 30.

Acquiring a request command for removing an inter-station link to thewireless base station Y 30, the removal request determining section 533determines whether an inter-station link has been set to the wirelessbase station Y 30 (S401). Specifically, the removal request determiningsection 533 refers to the inter-station link setting information of thewireless base station Y 30 stored in the wireless base stationinformation 150, so as to determine whether the inter-station linksetting information indicates “set” or “unset”.

If the inter-station link setting state of the wireless base station Y30 is not “set” (NO at S401), the removal request determining section533 determines that removal of the inter-station link is “not required”(S402). Because the link has been established to the wireless basestation Y 30, the removal request determining section 533 terminates theprocess for determining an inter-station link removal request.

On the contrary, if the inter-station link setting state of the wirelessbase station Y 30 is “set” (YES at S401), the removal requestdetermining section 533 determines whether the number of X2 handoversmade to the wireless base station Y 30 is equal to or less than apredetermined number (S403). Specifically, the removal requestdetermining section 533 refers to the number of X2 handovers made to thewireless base station Y 30 stored in the handover execution information160, so as to determine whether the number of the performed X2 handoversis equal to or less than a predetermined number, for example, not morethan two.

When the number of the performed X2 handovers exceeds two (NO at S403),the removal request determining section 533 determines that removal ofthe inter-station link is “not required” (S402). In this case, X2handover is performed frequently, and if the inter-station link isremoved and switched to S1 handover, the processing load is imposed onthe EPC 20. Thus, the process for determining an inter-station linkremoval request is terminated.

On the contrary, if the number of the performed X2 handovers is equal toor less than two (YES at S403), X2 handover is not performed frequently.In this case, even if the inter-station link is removed and switched toS1 handover, no processing load is imposed on the EPC 20. Thus, theremoval request determining section 533 determines that removal of aninter-station link is “required” (S404), and terminates the process fordetermining an inter-station link removal request.

When removal of the inter-station link is “required”, the removalrequest determining section 533 outputs an inter-station link removalrequest made to the wireless base station Y 30 to the removal requestingsection 541. The removal requesting section 541 outputs theinter-station link removal request made to the wireless base station Y30, to the wireless base station Y 30 through the wired transmitting andreceiving unit 120. Accordingly, the wireless base station Y 30 removesthe inter-station link.

In this way, the wireless base station X 10 can dynamically remove andset an inter-station link to the wireless base station Y 30. Thisprevents an increase in the processing load on the EPC 20 caused byexecution of S1 handover. Further, by removing the inter-station link tothe wireless base station Y 30, the wireless base station X 10 releasesresources necessary for setting the inter-station link. This enablesefficient use of the resources allocated to inter-station link.

According to the second embodiment, when the mobile communicationterminal 40 makes a request to switch a communication recipient from thewireless base station X 10 to the wireless base station Y 30, thewireless base station X 10 determines whether an inter-station link hasbeen set to the wireless base station Y 30. As a result, if nointer-station link has been set to the wireless base station Y 30, thewireless base station X 10 acquires the setting information necessaryfor setting an inter-station link to the wireless base station Y 30,from the wireless base station Y 30 through the EPC 20. Based on theacquired setting information of the wireless base station Y 30, thewireless base station X 10 requests the wireless base station Y 30 toset an inter-station link thereto. Further, the wireless base station X10 counts the number of S1 handovers or the number of X2 handovers, madeby a plurality of mobile communication terminals from the currentwireless base station X 10 to the wireless base station Y 30. Thewireless base station X 10 then determines whether the number ofperformed X2 handovers exceeds a predetermined number. If the number ofperformed X2 handovers does not exceed the predetermined number, thewireless base station X 10 requests the wireless base station Y 30 toremove the inter-station link.

In this way, the wireless base station X 10 can dynamically remove andset an inter-station link to the wireless base station Y 30. Thisprevents an increase in the processing load on the EPC 20 caused byexecution of S1 handover. Further, by removing the inter-station link tothe wireless base station Y 30, the wireless base station X 10 releasesthe resources necessary for setting the inter-station link. This enablesefficient use of the resources allocated to inter-station link.

As to the processing functions implemented in the wireless base stationsX 10 and Y 30, all or any portion of the functions may be implemented bya program interpretable and executable by a central processing unit(CPU), or may be implemented in hardware using wired logic. Further,such a program may be stored in a computer readable medium.

All examples and conditional language recited herein are intended forpedagogical purposes to aid the reader in understanding the inventionand the concepts contributed by the inventor to furthering the art, andare to be construed as being without limitation to such specificallyrecited examples and conditions, nor does the organization of suchexamples in the specification relate to a showing of the superiority andinferiority of the invention. Although the embodiment(s) of the presentinventions have been described in detail, it should be understood thatthe various changes, substitutions, and alterations could be made heretowithout departing from the spirit and scope of the invention.

1. A base station apparatus comprising: a processor; and a memory,wherein the processor executes: first determining whether a direct linkhas been established between the base station apparatus and another basestation apparatus, when a mobile device makes a request to switch acommunication recipient from the base station apparatus to the otherbase station apparatus; acquiring, indirectly from the other basestation apparatus, link information necessary for establishing thedirect link to the other base station apparatus, when the firstdetermining determines that no direct link to the other base stationapparatus has been established; first requesting the other base stationapparatus to establish the direct link to the base station apparatus,based on the link information of the other base station apparatusacquired by the acquiring; counting a number of handovers made using thedirect link to the other base station apparatus established in responseto the first requesting, or a number of handovers made using an indirectlink to the other base station apparatus, the handovers being made by aplurality of mobile devices each switching a communication recipientfrom the base station apparatus to the other base station apparatus; andsecond determining whether the number of handovers counted by thecounting and made using the indirect link to the other base stationapparatus exceeds a predetermined number, wherein the first requestingrequests the other base station apparatus to establish the direct linkto the base station apparatus, when the second determining determinesthat the number of handovers made using the indirect link to the otherbase station apparatus exceeds the predetermined number.
 2. The basestation apparatus according to claim 1, wherein the processor furtherexecutes: third determining whether the number of handovers counted bythe counting and made using the direct link to the other base stationapparatus exceeds the predetermined number; and second requesting theother base station apparatus to cancel a link to the base stationapparatus, when the third determining determines that the number ofhandovers made using the direct link to the other base station apparatusdoes not exceed the predetermined number.
 3. The base station apparatusaccording to claim 2, wherein the third determining determines whetherthe number of handovers made using the direct link to the other basestation apparatus exceeds the predetermined number, when the countingfinds an increase in counted handovers made using the direct link to theother base station apparatus.
 4. The base station apparatus according toclaim 1, wherein the processor further executes storing the linkinformation of the other base station apparatus acquired by theacquiring, wherein the first requesting requests the other base stationapparatus to establish the direct link to the base station apparatusbased on the link information of the other base station apparatus storedby the storing, when the second determining determines that the numberof handovers made using the indirect link to the other base stationapparatus exceeds the predetermined number.
 5. The base stationapparatus according to claim 1, wherein the second determiningdetermines whether the number of handovers made using the indirect linkto the other base station apparatus exceeds the predetermined number,when the counting finds an increase in counted handovers made using theindirect link to the other base station apparatus.
 6. A communicationcontrol method performed by a communication control system comprising afirst base station apparatus with which a mobile device is in wirelesscommunication; a second base station apparatus neighboring the firstbase station apparatus; and a control device connected to the first andthe second base station apparatuses, the communication control methodcomprising: first determining whether a direct link has been establishedto the second base station apparatus, when the mobile device makes arequest to switch a communication recipient from the first base stationapparatus to the second base station apparatus; acquiring, from thesecond base station apparatus through the control device, linkinformation necessary for establishing the direct link to the secondbase station apparatus, when, in the first determining, it is determinedthat no direct link to the second base station apparatus has beenestablished; and first requesting the second base station apparatus toestablish the direct link to the first base station apparatus, based onthe link information of the second base station apparatus acquired inthe acquiring; counting a number of handovers made using the direct linkto the second base station apparatus established in response to thefirst requesting, or a number of handovers made using an indirect linkto the second base station apparatus, the handovers being made by aplurality of mobile devices each switching a communication recipientfrom the first base station apparatus to the second base stationapparatus; and second determining whether the number of handoverscounted by the counting and made using the indirect link to the secondbase station apparatus exceeds a predetermined number, wherein the firstrequesting requests the second base station apparatus to establish thedirect link to the first base station apparatus, when the seconddetermining determines that the number of handovers made using theindirect link to the second base station apparatus exceeds thepredetermined number.
 7. An inter-station control method comprising:first determining whether a direct link has been established between abase station apparatus and another base station apparatus, when a mobiledevice makes a request to switch a communication recipient from the basestation apparatus to the other base station apparatus; acquiring,indirectly from the other base station apparatus, link informationnecessary for establishing the direct link to the other base stationapparatus, when, in the first determining, it is determined that nodirect link to the other base station apparatus has been established;and first requesting the other base station apparatus to establish thedirect link to the base station apparatus, based on the link informationof the other base station apparatus acquired in the acquiring counting anumber of handovers made using the direct link to the other base stationapparatus established in response to the first requesting, or a numberof handovers made using an indirect link to the other base stationapparatus, the handovers being made by a plurality of mobile deviceseach switching a communication recipient from the base station apparatusto the other base station apparatus; and second determining whether thenumber of handovers counted by the counting and made using the indirectlink to the other base station apparatus exceeds a predetermined number,wherein the first requesting requests the other base station apparatusto establish the direct link to the base station apparatus, when thesecond determining determines that the number of handovers made usingthe indirect link to the other base station apparatus exceeds thepredetermined number.